SG versus Glass Thickness

Discussion in 'General Discussions and Advice' started by Tiger eye, 22 Aug 2012.

  1. Tiger eye

    Tiger eye

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    Hi guys i've got a question for you.
    If a tank of 1,2m x 450mm x 450mm x 6mm glass is sufficient for fresh water with NO extra bracing. Why are whe bulding the same size with 10mm glass or bracing the heck out of it and making the tank look ugley. If I understand Specific Gravity (SG) corectley that means that theoreticaly 1ml of RO water (pure water) weighs 1g that has a SG of 1,000. So a tank of 1200mm x 450mm x 450mm wil have a volume of 243 litre.If SG is 1,000 the water wil weigh 243kg and at SG 1,025 it wil weigh 249kg so its an increse of 6kg in total. ime not talking about the base that has to cary the sand and live rock aswel but the sides that onley handels water pressure. My question is are we obsessing about glass thikness that is not realy nessesary and just ading to the cost of our tanks just becorse its a "Marine" Tank so it has to be more expensive with thick glass and bracing and cross brasing ect ect... is it not more of a stigma conected to salt water that it is hevier than fresh water but nobody stops and thinks is (in this case) 6KG in total (and not per squere inch) nesesery to either jump to 10mm if you want to go rimless or brace the heck out of it.

    Please corect me if I am wrong but this is my understanding.
     
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  3. mornewil

    mornewil Morne

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    Im no expert but i would think that the weight of your liverock & corals adds up a whole lot more as to fw where you have a bunch of plants with few rocks, driftwood, plastic ornaments etc etc. Also the flow in a marine tank is usually more hectic than in a fw tank adding pressure on the glass.
    Just my 'logically thinking' opinion on the matter.
    Then again people may just take extra precaution with marine tanks as there goes alot more money into it than a fw tank.
    Lets see what the experts say...
     
  4. Tiger eye

    Tiger eye Thread Starter

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    I agree with you about the live rock but that weight is on the base and not he sides. That only takes water presure.
     
  5. viper357

    viper357 Admin MASA Contributor

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    I'm no tank builder but in my opinion 10mm for a 4ft tank is overkill. I had a 1.2 x 45 x 45 that was made out of 6mm glass, although it did have a center brace. It's all still in one piece today. :)
     
    Last edited: 22 Aug 2012
  6. Quintin

    Quintin

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    It all depends if you want to run a wave maker / wave box in the tank or just normal flow pumps.
    Remember waves will shift the weight of the water around the tank much more than a simple flow pump and even one little MP10 set at the right frequency will demolish your tank plus stand in wave motion if the tank is not built to handle the pressure.

    Personally I would rather spend a bit more and do a proper build that skimp it now and suffer down the line with a rebuild.

    Buy the best you can afford at this stage to make sure you wont regret it down the line, is my opinion.
    Shop around and see what different tank builders quote you.
    Also have a look at what they have built in the past as this will give you an idea on quality and finish.
     
    Last edited: 22 Aug 2012
  7. Bob the (reef)builder

    Bob the (reef)builder

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    There is no material difference that anyone worries about regarding differences re SG.

    However, even though that fw tank might hold together, I would certainly not want it in my home. It's pretty dodgy and one decent bump could cause a lot of water on your floor.

    The bracing is what makes the big difference to the stability.

    I would start to think about a shallow tank like that unbraced at about 10mm thick.

    It's just silly to skimp on glass thickness if you consider the investment in time, energy and money we put into our tanks.

    Cheers
    Rob.

    Added after Quintin's post: If I was doing it for a wave type tank, I would probably go with 12mm as this adds hugely to the stresses.
     
    Last edited: 22 Aug 2012
  8. Jayceew

    Jayceew

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    Agree with Rob here, I dont think it's so much the differences in weight but rather difference in investment that we are trying to protect.

    I had a 600l freshwater tank that burst in my house a couple of years back, total damage: R7000. If that was a marine tank...
     
  9. vatso

    vatso

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    Let's have a look at the problem

    Water pressure which is the issue is equal in every direction at depth the deeper the more equal pressure.

    So will it hold the water weight / pressure yes. Here is the catch salt water has lots of flow in it which creates additional pressure which fresh water does not have.
     
  10. RiaanP

    RiaanP Moderator

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    Take a standard Daro 90cm tank. It is not braced. Fill it to the top and measure the width of the tank in the middle compared to the ends. Looking lengthwise down that tank and you will wonder how the tank stay together. OK, the DARO is not 6mm but still, you can see the distance the front and back panel bow outwards.

    Last time I did this, the long panes bowed each by about 5 to 6mm. Yikes. Imagine lifting a rock out and slightly bumping the pane....
     
  11. Tiger eye

    Tiger eye Thread Starter

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    Thank you for replying and helping me understand.
    Just to make sure it is more about investment protection than actual water presure exept if you go the wavemaker root then the thick glas is a must not a option.

    I am in the situation were I absolutely love this hobby but but have other responsebilatys and can not just splash out R3500 - R4500 or more on a upgrade to a butifull 4ft rimless. Ime pretty skild at DIY so that makes it easier. Found out that 10mm glass for a 4ft tank wil cost me +-R3500 if I build it myself and that is not talking about the stand. So I looked at the FW tanks and it was R1400 so I started wondering why must a marine tank be made of such thick glass.
     
  12. vatso

    vatso

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    Any water movement will cause pressure not just a wave maker
     
  13. Wes

    Wes

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    @Tiger eye chat to @yingyang last i heard he had some cubes for sale.
     
    Last edited by a moderator: 26 Nov 2015
  14. Bob the (reef)builder

    Bob the (reef)builder

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    This is true but the difference between normal wter pumps and a standing wave going back and forth is massive. the whole tank sways from side to side a little.
     
  15. vatso

    vatso

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    100% correct bob in fact I agree with your post

    I just don't want the answer to be missed flow pumps increase pressure in a tank
     
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